This invention is concerned with the measurement of the characteristics of a device under test (DUT).
Generally the impedance, gain or phase shift or quality of a DUT, for example a resistor, capacitor, amplifier, or a digital to analog converter, can be measured by providing an A.C. test signal input to the DUT and then comparing that input signal with the A.C. output signals from the DUT or analyzing the A.C. output signal of the DUT. For measurement with high frequency test signals, it may be necessary to convert the high frequency output signal from the DUT to a lower intermediate frequency signal using a selected local oscillator signal. In prior art, making accurate high frequency measurements was difficult and required complicated circuits, especially the circuit for generating the desired local oscillator signal.